Hypsometer



June 1966 P. A. ROGERS ETAL 3,254,535

HYPSOMETER Filed Sept. 19, 1963 5 v4 5 I! 5 ii if a! I! F I! v! I! 5 I as mm R Ae P Rum IC H I PM IN VENTORS A T'roRNE Y5 Q/QZM MAQ United States Patent 3,254,535 HYPSOMETER Philip A. Rogers and Lucien B. Brooks, Baltimore, Md., assignors to The Bendix Corporation, Baltimore, Md., a corporation of Delaware 7 Filed Sept. 19, 1963, Ser. No. 309,973

8 Claims. (Cl. 73384) This invention relates to an improved type of hypsometer.

In the high altitude radiosondes presently in use, there are two means for converting atmospheric pressure to a signal indicating altitude. One such means is a pressure capsule having a metallic diaphragm responsive to pressure changes. This capsule provides pressure signals with acceptable accuracy only up to a given height, such as 50,000 ft. Above this height a hypsometer begins to function and this device may extend the range up to heights of the order of 100,000 ft. or more. Such'hypsometers have been in use for many years. The typical hypsometers presently. in use consist of a container into which is placed a small quantity of a known liquid having certain desirable specific heat qualities such as car- 'bon disulfide. A thermistor inserted into the container is kept in contact with the evaporating liquid about its surface by means of a wick or capillary member which is held in contact with said thermistor. As the radiosonde reaches a given high altitude, a pressure is reached at which the carbon disulfide begins to boil. As the altitude increases further and the ambient pressure is correspondingly decreased, boiling takes place at lower and lower temperatures, and these temperatures are sensed by the thermistor which is connected into an electrical circuit which provides an input to the transmitter.

- Because the continued boiling of the carbon disulfide is dependent upon the retention of heat during ascent, the container used has been a Dewar flask or miniature vacuum bottle having an evacuated space between two layers'of silvered glass. The use of such containers has some disadvantages in that they are fragile and easily broken either during assembly or during shipping and subsequent handling prior to launch. Special provisions must be made, therefore, to protect these flasks frombeing broken. A further drawback is that such flasks constitute one of the most expensive components in the entire radiosonde. Despite these disadvantages, the operation of the Dewar flask has been sufliciently satisfactory that large numbers have been supplied for this use.

Another source of difiiculties in manufacturing of hypsometers of this type is the dexterity required to attach the wick or capillary member to the thermistor. The wick used is usually a strip of cotton which is twisted around one end of the thermistor which is usually bent to form a 45 bend, permitting one end to hang free so that it can be immersed in the carbon disulfide. one function of the Wick is to prevent breakage of the thermistor by preventing it from striking the side of the flask. Often the wick does not remain secured to the thermistor during assembly, and sometimes the thermistor is broken. This has led to substantial expense in requiring extra inspections and rework operations on the assembly line. Additional expense is involved in requiring that the thermistor be made hooked or bent, rather than straight. It is an object of the present invention, therefore, to provide a hypsometer of the type described which can be manufactured at substantially less cost that those presently in use.

It is another object of the present invention to provide a hypsometer of the type described which is simpler and easier to build than those presently in use.

' It is another object of the present invention to provide a hypsometer of'the type described in which losses due to breakage of the container or the thermistor are substantially reduced.

Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings, in which:

FIG. 1 is a sectional view of a hypsometer assembly manufactured according to our invention; and

FIG. 2 is a sectional view of another embodiment of our invention.

Referring now to FIG. 1, a hypsometer assembly is shown generally at numeral 10 and includes a cylindrical flask 12 of a solid plastic material such as a plastic polycarbonate which is encased in a resilient insulating container 14 of a material such as polyethylene foam. Fitted tightly to the top of flask 12 is a plastic cap member 16 which carries a thermistor 18 consisting of a length of resistance wire encased in glass, and a pair of electrical terminals 20 and "22 to vwhich the ends of the resistance wire are attached. Cup 16 also includes a port 24 providing communication between the interior of the flask and the atmosphere. 7

The flask 12 is normally filled to approximately twothirds or three-quarters of its capacity with a liquid selected for its desirable specific heat characteristics, such as carbon disulfide. Carried in -the bottom of the' flask 12 is a capillary member 26 which is a block of an open cellular type of plastic such as polyurethane. The thermistor 18 is pushed some distance into this foam member 26 which provides the functions of assuring some contact of the thermistor 18 with the liquid even thoughrthe supply of liquid drops below the level of the thermistor in the flask, and assuring adequate lateral and vertical support, thereby preventing the thermistor from being damaged by vibration or shock forces which might otherwise cause it to hit against the side of the flask.

It has been found that the use of the solid plastic flask permits easier and simpler assembly operations than the Dewar flask previously used because of its ruggedness and durability. The heat transfer characteristic is not quite so good as that of the Dewar flask, but it is within acceptable limits such that the structural advantages far outweigh the slight loss in insulation quality. A

substantial reduction cost accompanies these structural advantages, making the plastic flask quite attractive for this application. Still further advantages are realized by the use of the straight thermistor .18, the inner end of which is pushed into the polyurethane capillary member 26. This avoids many of the sources of difliculties in assembly referred to above where the thermistor used is hooked or bent to permit attachment of a cotton wick which is wrapped around the hooked portion, and provides both lateral and vertical support for the said inner end.

A modified form of the invention is shown in FIG. 2. In this embodiment all of the pants are the same as those of FIG; 1 and are numbered the same except for the flask 12a, which is constructed of two parts 28 and 30 of plastic material which may be the same as that of flask 12. The part 28 is adapted to fit inside of part 30, such that a dead air space 32 of some significant width (perhaps ,4 inch) is maintained between the said parts. This arrangement affords essentially the same advantage of ruggedness as the FIG. 1 embodiment and is only slightly more expensive to manufacture. It does provide better insulating qualities than the solid flask and has been found to exceed the heat transfer qualities of the Dewar flask. Where even better insulating qualities are I desired, one or both of the surfaces of parts 28 and 30 which adjoin the dead air space 32 may be silvered.

From the foregoing it will be appreciated that the arrangement described herein affords substantial advantages J over the prior art. These advantages appear in very substantially lower costs "for the final product, both as a result of the lower cost of the plastic flasks vs. the glass Dewar flasks and the straight thermistor vs. the bent thermistor as well as the lower production costs due to the simpler assembly made possible by the plastic foam capillary member. Further advantages are afforded by the inherently more rugged hypsometer design whic minimizes losses in shipment and handling.

While only two embodiments have been shown and described herein, these are to be considered exemplary only and it is recognized that modifications may be made within the scope of the present invention.

We claim:

1. A hypsometer comprising:

a cylindrical flask member of plastic material adapted to receive a supply of liquid,

a cap member -for said flask having a passageway communicating the inside of said flask with the atmosphere and electrical contact means supported by said p,

a capillary member positioned near the bottom of said flask,

and an elongated thermistor member supported at one end by said cap and extending into the interior of said flask suchthat its opposite end is at least laterally supported by said capillary member and wires connected between said thermistor and said electrical contact means.

2. A hypsometer comprising:

a cylindrical flask member of plastic material adapted to receive a supply of liquid,

a cap member for said flask having a passageway communicating the inside of said flask with the atmosphere and electrical contact means supported by said p,

a capillary member positioned near the bottom of said flask consisting of a block of substantially rigid open cellular foam material,

and an elongated thermistor member supported at one end by said cap and extending into the interior of said flask such that its opposite end extends into and is supported by said capillary member,

and electrical connections between said thermistor and said electrical contact means.

3. A hypsometer comprising:

a cylindrical flask member of plastic material adapted to receive a supply of liquid, said flask having a single layer wall of substantial thickness,

a cap member for said flask having a passageway communicating the inside of said flask with the atmosphere and electrical contact means supported by said cap,

a capillary member positioned near the bottom of said flask consisting of open cellular foam material,

an elongated thermistor member supported at one end by said cap and extending into the interior of said flask such that its opposite end extends into and is supported by said capillary member,

and connections between said thermistor and said electrical contact means.

4. A hypsometer as set forth in claim 3 wherein said flask is substantially enclosed in a container of resilient plastic foam material.

5. A hypsometer comprising:

a cylindrcal flask member of plastic material adapted to receive a supply of liquid, said flask having a single layer wall of substantial thickness,-

a cap member for said flask having a passageway communicating the inside of said flask with the atmosphere and a pair of electrical contact means supported by said cap,

a capillary member positioned near the bottom of said flask consisting of a block of substantially rigid open cellular plastic foam material,

an elongated thermistor member supported at one end by said cap and extending into the interior of said flask such that its opposite end extends into and is supported by said capillary member,

and electrical connections between said thermistor and said electrical contact members.

6. A hypsometer comprising:

a cylindrical flask member of plastic material adapted to receive a supply of liquid, said flask being made of two layers of plastic material enclosing a dead air space therebetween,

a cap member for said flask having a passageway communicating the inside of said flask with the atmosphere and a pair of electrical contact means supported by said cap,

a capillary member positioned near the bottom of said flask consisting of a block of substantially rigid open cellular plastic foam material,

an elongated thermistor member supported at one end by said cap and extending into the interior of said flask such that its opposite end extends into and is supported by said capillary member,

and connections between said thermistor and said electrical contact members.

7. A hypsometer as set forth in claim 6 wherein said flask in substantially enclosed in a container of resilient plastic foam material.

8. A hypsometer as set forth in claim 6 wherein at least one of said two layers of said plastic material is silvered on the side adjacent said dead air space.

References Cited by the Examiner UNITED STATES PATENTS 2,832,219 4/1958 Sapoff et al. 73384 DAVID SCHONBERG, Acting Primary Examiner. 

2. A HYPOSOMETER COMPRISING: A CYLINDRICAL FLASK MEMBER OF PLASSTIC MATERIAL ADAPTED TO RECEIVE A SUPPLY OF LIQUID, A CAP MEMBER FOR SAID FLASK HAVING A PASSAGEWAY COMMUNICATING THE INSIDE OF SAID FLASH WITH THE ATMOSPHERE AND ELECTRICAL CONTACT MEANS SUPPORTED BY SAID CAP, A CAPILLARY MEMBER POSITIOINED NEAR THE BOTTOM OF SAID FLASK CONSISTING OF A BLOCK OF SUBSTANTIALLY RIGID OPENCELLULAR FOAM MATERIAL, AND AN ELONGATED THERMISTOR MEMBER SUPPORTED AT ONE END BY SAID CAP AND EXTENDING INTO THE INTERIOR OF SAID FLASK SUCH THAT ITS OPPOSITE END EXTENDS INTO AND IS SUPPORTED BY SAID CAPILLARY MEMBER, AND ELECTRICAL CONNECTIONS BETWEEN SAID THERMISTOR AND SAID ELECTRICAL CONTACT MEANS. 